My invention relates to security systems and particularly to security systems which combine the advantages of low cost reliable integrated circuits and a microcomputer to attain the advantages of cryptographic encoding at minimum expense and complication.
Security systems employing electro-mechanical bolts or locks, controlled by electrical circuits requiring a combination of electrical inputs for unlocking, are well known in the art. Many of these systems employ wired digital logic to insure that only a proper combination of inputs will operate the locking mechanism. Such systems are complex to design and manufacture and would require extensive physical wiring changes to change the combinations of inputs required to unlock the system.
Also, prior systems have relied on a single number value, generally encoded in binary form, such as an 8-bit combination which would provide the equivalent of decimal numbers from 0 to 256 (28). Such arrangements can be rather easily defeated, since it is relatively simple to build a circuit arrangement which will quickly generate a sequence of all of the possible combinations, and by supplying this sequence to the security systems input, the unlocking sequence will be quickly found. More secure systems relay on such binary coded numbers and/or a set or keyboard entered numbers which must be remembered by the user, such as with card entry systems. U.S. Pat. Nos. 3,821,704; 4,286,305 and Re. 29,846 are exemplary of such prior art.